If Leads created by Soapbox Engage apps are autocoverting in your Salesforce instance but the subesquent Opportunity being created doesn't have values for the Close Date, Amount, and other expected fields, there are few things that could be the cause Here's a few troubleshooting steps to check to get things working properly.
1) Confirm that your Salesforce instance is processing triggers during lead conversion. This can be found (with the Enhanced User Interface setting enabled) under Setup > Build > Customize > Leads > Settings > Lead Conversion Settings > Require Validation for Converted Leads". This box should be checked. If not, check it. If this option doesn't exist, contact your Salesforce support representative to have "Use Apex Lead Convert" turned on.
Please note that it is possible that the close date IS getting filled in. This does not mean that this is not the underlying issue. Instead it may mean that there is a default close date being set on the account for opportunities.
Finally, when editing this setting there is also a "Record Type Setting". The options for this are to either "Keep the existing record type" or "Override the existing record type with the assignee's default record type". Either of these options should work.
2) Confirm that the user account that is tied to your Soapbox Engage site has access to the correct Soapbox Engage record types